1. Field of the Invention
The present invention relates to an image forming apparatus and an image forming method, and more particularly, to technology for increasing the viscosity of ink or solidifying (curing) ink by means of a two-liquid reaction between ink and a transparent treatment liquid, and thereby preventing deposition interference between inks, bleeding into the recording medium, bleeding due to overlapping of ink droplets of different colors, and the like.
2. Description of the Related Art
Inkjet recording apparatuses (inkjet printers) having an inkjet head (ink ejection head) in which a plurality of nozzles are arranged, are known as image forming apparatuses. An inkjet recording apparatus of this kind forms images by forming dots on a recording medium, by ejecting ink as droplets from nozzles, while causing the inkjet head and the recording medium to move relatively to each other.
Various methods are known as ink ejection methods for an inkjet recording apparatus of this kind. For example, one known method is a piezoelectric method, where the volume of a pressure chamber (ink chamber) is changed by causing a diaphragm forming a portion of the pressure chamber to deform due to deformation of a piezoelectric element (piezoelectric actuator), ink being introduced into the pressure chamber from an ink supply passage when the volume is increased, and the ink inside the pressure chamber being ejected as a droplet from the nozzle when the volume of the pressure chamber is reduced. Another known method is a thermal inkjet method where ink is heated to generate a bubble in the ink, and ink is then ejected by means of the expansive energy created as the bubble grows.
In an inkjet recording apparatus, one image is represented by combining dots formed by ink ejected from the nozzles. In this case, it has been proposed that image quality can be improved, by mixing together two liquids, namely, transparent treatment liquid and ink, thereby increasing the viscosity of the ink or solidifying the ink, and thus preventing bleeding into the recording medium, or bleeding due to overlapping between ink droplets.
For example, a method is known in which it is sought to improve the quality of a recorded image by providing a device which applies a coating material (treatment liquid) onto a recording medium in accordance with a recording signal, before recording by means of the recording ink has been performed onto the recording medium, the coating material being deposited only onto the ink droplet deposition region of the recording medium, or alternatively, the droplet deposition density of the coating material being reduced below the droplet deposition density of the ink (see, for example, Japanese Patent Application Publication No. 6-255096).
Furthermore, for example, a method is also known in which an inkjet head which ejects treatment liquid that causes the coloring material in the ink to become insoluble or to aggregate is provided in addition to an inkjet head which ejects ink, and the recording region of the recording medium is divided up into blocks, no droplets of treatment liquid being deposited in a block where not one droplet of ink is to be deposited, and droplets of treatment liquid being deposited in a prescribed uniform droplet deposition pattern in a block where droplets of ink are to be deposited. Thereby, good water resistance is obtained in the recorded image, and furthermore, the image recording is free from bleeding at the boundaries between different colors (see, for example, Japanese Patent Application Publication No. 8-72231).
Moreover, for example, a method is known in which, when a prescribed number or more of ejection data for ejecting recording ink are present in recording data which corresponds to respective recording blocks obtained by dividing the recordable region of the recording medium into a plurality of regions, then a treatment liquid which causes the coloring material inside the recording ink to become insoluble or to aggregate is deposited over the whole area of that recording block, or alternatively, treatment liquid is deposited in a certain specified pattern which corresponds to the number of ink droplets to be deposited. In this way, excellent image quality is achieved while suppressing the amount of treatment liquid consumed. (See, for example, Japanese Patent Application Publication No. 8-72233).
As described above, in an inkjet printer based on a two-liquid reaction which prevents deposition interference between inks or bleeding by mixing treatment liquid and ink together and causing the ink to increase in viscosity or to solidify as a result of reaction between the two liquids, it has been proposed that the amount of treatment liquid used be restricted by dividing the image region on the recording medium up into blocks and deciding whether or not to deposit droplets of treatment liquid with respect to each block individually, on the basis of the recording data, with the object of reducing running costs and reducing the amount of treatment liquid and ink solvent, and so on. The condition for judging whether or not to deposit droplets of treatment liquid in each block is based on determining whether one or more droplet of ink is to be deposited in that block, or whether no ink droplet is to be deposited in that block (see, for example, Japanese Patent Application Publication Nos. 6-255096 and 8-72231), or this judgment is made by determining whether or not a prescribed number of more of ink droplets are to be deposited, without making any distinctions between the size of the ink droplets, or the like (see, Japanese Patent Application Publication No. 8-72233). Here, deposition interference refers to shifting of the dot formation positions from the prescribed landing position (the position of the liquid droplet upon landing) and/or disturbance of the dot shapes, due to coalescence between mutually adjacent liquid droplets on the recording medium.
However, in the case of extremely simple judgment conditions of this kind, there is a problem in that suitable judgment cannot be made in order to prevent image deterioration caused by deposition interference, bleeding into ordinary paper, bleeding between colors, and the like.